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Description: Regional precipitation patterns may have influenced the spatial variability of tree mortality during the recent mountain pine beetle (Dendroctonus ponderosa) (MPB) outbreak in the western United States. Data from the Forest Inventory and Analysis (FIA) Program show that the outbreak was especially severe in the state of Colorado where over 10 million lodgepole pines (Pinus contorta Dougl. Ex Loud.) succumbed to MPB between 2002 and 2009. Aerial detection maps of MPB-related mortality show that the infestation was initially widespread and evenly distributed throughout the range of lodgepole pine in Colorado, but gradually became more severe in the northern portion of the state. Because southern Colorado receives relatively high summer precipitation due to the effects of the North American monsoon (NAM), the spatial pattern of MPB-related mortality suggests that infestation severity was lower in areas with the higher summer precipitation. This study investigated the link between lodgepole pine mortality due to MPB and seasonal precipitation patterns associated with the NAM in Colorado. Data regarding insect-related tree mortality and damage data were summarized from FIA data collected between 2002 and 2009, and gridded precipitation data were acquired from the North American Regional Reanalysis Project. Results indicated that while absolute NAM-related precipitation was not an important predictor of infestation severity, the deviation of a five-year average of summer and fall precipitation relative to climatic means was important.